{"id":"UBUNTU-CVE-2026-55717","details":"In NLnet Labs Unbound 1.10.0 up to and including 1.25.1, when 'serve-expired: yes' is set together with a 'response-ip: \u003cnet\u003e redirect' /'response-ip-data: \u003cnet\u003e CNAME \u003ctarget\u003e' rule (or the RPZ 'rpz-cname-override' equivalent), a remote client who controls any delegated domain can crash the daemon. The serve-expired-client-timeout callback runs a two-pass loop to chase the respip-generated CNAME alias; on the second pass it resets 'alias_rrset' but not 'partial_rep'. Later, this inconsistency leads to a NULL pointer dereference and an eventual crash. A malicious actor can exploit the vulnerability by controlling any zone that replies with an A/AAAA record that falls inside the configured response-ip/rpz subnet. By delaying the answer when the previous record has expired, the vulnerable path of 'serve-expired-client-timeout' is taken leading to denial of service via the server crash.","modified":"2026-08-20T23:15:22.574567733Z","published":"2026-07-22T14:17:00Z","upstream":["CVE-2026-55717"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-55717"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-55717"},{"type":"REPORT","url":"https://community.nlnetlabs.nl/t/unbound-1-25-2-released/3430"}],"affected":[{"package":{"name":"unbound","ecosystem":"Ubuntu:Pro:14.04:LTS","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra-legacy%2Ftrusty"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.4.20-1","1.4.21-1","1.4.21-1ubuntu1","1.4.21-1ubuntu2","1.4.22-1ubuntu1","1.4.22-1ubuntu2","1.4.22-1ubuntu3","1.4.22-1ubuntu4","1.4.22-1ubuntu4.14.04.1","1.4.22-1ubuntu4.14.04.2","1.4.22-1ubuntu4.14.04.3","1.4.22-1ubuntu4.14.04.3+esm1","1.4.22-1ubuntu4.14.04.3+esm2","1.4.22-1ubuntu4.14.04.3+esm3"],"ecosystem_specific":{"binaries":[{"binary_version":"1.4.22-1ubuntu4.14.04.3+esm3","binary_name":"libunbound2"},{"binary_version":"1.4.22-1ubuntu4.14.04.3+esm3","binary_name":"python-unbound"},{"binary_name":"unbound","binary_version":"1.4.22-1ubuntu4.14.04.3+esm3"},{"binary_name":"unbound-anchor","binary_version":"1.4.22-1ubuntu4.14.04.3+esm3"},{"binary_name":"unbound-host","binary_version":"1.4.22-1ubuntu4.14.04.3+esm3"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-55717.json"}},{"package":{"name":"unbound","ecosystem":"Ubuntu:Pro:16.04:LTS","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra-legacy%2Fxenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.4.22-1ubuntu6","1.5.7-1ubuntu1","1.5.7-1ubuntu2","1.5.8-1ubuntu1","1.5.8-1ubuntu1.1","1.5.8-1ubuntu1.1+esm1","1.5.8-1ubuntu1.1+esm2","1.5.8-1ubuntu1.1+esm3"],"ecosystem_specific":{"binaries":[{"binary_version":"1.5.8-1ubuntu1.1+esm3","binary_name":"libunbound2"},{"binary_name":"python-unbound","binary_version":"1.5.8-1ubuntu1.1+esm3"},{"binary_version":"1.5.8-1ubuntu1.1+esm3","binary_name":"unbound"},{"binary_name":"unbound-anchor","binary_version":"1.5.8-1ubuntu1.1+esm3"},{"binary_version":"1.5.8-1ubuntu1.1+esm3","binary_name":"unbound-host"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-55717.json"}},{"package":{"name":"unbound","ecosystem":"Ubuntu:Pro:18.04:LTS","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra%2Fbionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.6.5-1","1.6.7-1","1.6.7-1build1","1.6.7-1ubuntu1","1.6.7-1ubuntu2","1.6.7-1ubuntu2.1","1.6.7-1ubuntu2.2","1.6.7-1ubuntu2.3","1.6.7-1ubuntu2.4","1.6.7-1ubuntu2.5","1.6.7-1ubuntu2.6","1.6.7-1ubuntu2.6+esm2","1.6.7-1ubuntu2.6+esm3","1.6.7-1ubuntu2.6+esm4"],"ecosystem_specific":{"binaries":[{"binary_name":"libunbound2","binary_version":"1.6.7-1ubuntu2.6+esm4"},{"binary_version":"1.6.7-1ubuntu2.6+esm4","binary_name":"python-unbound"},{"binary_version":"1.6.7-1ubuntu2.6+esm4","binary_name":"python3-unbound"},{"binary_version":"1.6.7-1ubuntu2.6+esm4","binary_name":"unbound"},{"binary_name":"unbound-anchor","binary_version":"1.6.7-1ubuntu2.6+esm4"},{"binary_name":"unbound-host","binary_version":"1.6.7-1ubuntu2.6+esm4"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-55717.json"}},{"package":{"name":"unbound","ecosystem":"Ubuntu:Pro:20.04:LTS","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra%2Ffocal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.9.0-2ubuntu1","1.9.0-2ubuntu2","1.9.4-2","1.9.4-2ubuntu1","1.9.4-2ubuntu1.1","1.9.4-2ubuntu1.2","1.9.4-2ubuntu1.3","1.9.4-2ubuntu1.4","1.9.4-2ubuntu1.5","1.9.4-2ubuntu1.6","1.9.4-2ubuntu1.8","1.9.4-2ubuntu1.9","1.9.4-2ubuntu1.11","1.9.4-2ubuntu1.11+esm1"],"ecosystem_specific":{"binaries":[{"binary_version":"1.9.4-2ubuntu1.11+esm1","binary_name":"libunbound8"},{"binary_name":"python-unbound","binary_version":"1.9.4-2ubuntu1.11+esm1"},{"binary_version":"1.9.4-2ubuntu1.11+esm1","binary_name":"python3-unbound"},{"binary_name":"unbound","binary_version":"1.9.4-2ubuntu1.11+esm1"},{"binary_name":"unbound-anchor","binary_version":"1.9.4-2ubuntu1.11+esm1"},{"binary_version":"1.9.4-2ubuntu1.11+esm1","binary_name":"unbound-host"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-55717.json"}},{"package":{"name":"unbound","ecosystem":"Ubuntu:22.04:LTS","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=jammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.13.1-1ubuntu1","1.13.1-1ubuntu3","1.13.1-1ubuntu5","1.13.1-1ubuntu5.1","1.13.1-1ubuntu5.2","1.13.1-1ubuntu5.3","1.13.1-1ubuntu5.4","1.13.1-1ubuntu5.5","1.13.1-1ubuntu5.7","1.13.1-1ubuntu5.8","1.13.1-1ubuntu5.10","1.13.1-1ubuntu5.11","1.13.1-1ubuntu5.12","1.13.1-1ubuntu5.13","1.13.1-1ubu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